or Crystallized Carbonate of Lime, one of the most generally diversified substances in the mineral kingdom, and certainly that which presents the greatest variety of crystalline forms. The Abbé Haüy has drawn and described upwards of 500 of these; and since his time not fewer than 800 other distinct modifications have been determined, all of which, when fractured, present as their primitive form an obtuse rhomb of 105° 5' and 74° 55'. The most prevalent colour of calcareous spar is white, though it also presents numerous shades of yellow, green, blue, and red, most of them pale. Its dark brown and black colours are owing to the admixture of bitumen. It is transparent or translucent, and has in the clear specimens a very distinct double refraction. It has a vitreous lustre, and perfect cleavage. The pure varieties consist, according to the analyses of Stromeier, and Philips, of

- Lime: $56°15' - 55°50$ - Carbonic acid: $43°70' - 44°00'$

but the coloured ones not unfrequently contain small portions of oxide of iron, silica, magnesia, alumina, carbon, and bitumen. It effervesces violently with acids, and if pure is entirely soluble in nitric acid. At an ordinary heat it does not fuse, but gives off its carbonic acid, shines with a peculiar brightness, and ultimately becomes quick-lime. Among the most distinguished localities of calcareous spar may be enumerated Andreasberg and other mining districts in the Hartz, where the varieties in six-sided prisms have been found of great beauty; Alston Moor in Cumberland, which affords numerous flat rhombic crystals; and Derbyshire, whence the pyramidal forms, sometimes of very large dimensions, are obtained. Under the head of calcareous spar there are a number of sub-species, which depend chiefly upon their mode of composition, and upon admixtures and impurities, with which the individuals have been affected at their formation. These will be fully described among the minerals.